A number of drugs which depress nervous function (e.g., halothane, diphenylhydantoin and phenobarbital) and some which are classified as nonspecific anti-inflammatory agents (e.g., salicylates) have been shown to possess immunosuppressant activity. One of the major functions of an intact immune system is to recognize and destroy foreign tissue including cells undergoing somatic or viral transformation leading to malignancy. The objective of this study is to identify sites and mechanisms whereby phenobarbital and sodium salicylate suppress the immune system. We propose to study the effects of these two drugs on: 1) the mixed lymphocyte reaction in vitro; 2) the generation and activity of cytotoxic lymphocytes in vitro; 3) the mitogenic response of lymphocytes to phytohemagglutinin in vitro; 4) the response of bone marrow cells to colony stimulating factor in vitro as a measure of granulopoiesis; 5) the immunocompetence of human patients; and 6) the survival time of mice inoculated with transplantable tumors.